SEC Filings

genetic
modifier, who are able to sit but have no historical or current ability to stand or walk. One patient in this clinical trial has been dosed to date.

Two
dosage strengths will be evaluated and patients will be stratified into two age groups: patients less than 24 months and patients at least 24 months but less than
60 months. There will be at least a four-week interval between the dosing of the first three patients for each dose being studied and, based on the available safety data, a decision will be
made whether to proceed.

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Patients in Cohort 1 will receive a dose of 6.0 × 1013 vg of AVXS-101, or Dose A. Cohort 1 will consist
of three patients who are less than 24 months of age.

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If safety is established according to the Data Safety Monitoring Board, or the DSMB, the trial will proceed to Cohort 2.

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Patients in Cohort 2 will receive a dose of 1.2 X 1014 vg of AVXS-101, or Dose B. Cohort 2 will consist of three patients who are
less than 60 months of age.

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If safety is established according to the DSMB, an additional 21 patients will be enrolled until the trial includes a total of
(i) 12 patients less than 24 months of age and (ii) 12 patients at least 24 months, but less than 60 months, of age who have received Dose B.

According
to the well-characterized natural history of the disease by the Pediatric Neuromuscular Clinical Research Network, 100 percent of children with SMA Type 2 will
never walk without support, 95 percent of children will never stand without assistance and more than 30 percent will die by 25 years of age. Additionally, children with SMA
Type 2, who are between 24 and 60 months of age with 3 copies of the SMN2 gene, experienced a mean decrease of 0.33 points on the Hammersmith Function Motor Scale Expanded over a
12-month period at first evaluation.

Outcome Measures for Patients Less than 24 Months of
Age

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The primary outcome measure for patients less than 24 months of age at the time of dosing is the achievement of the ability to stand
without support for at least three seconds.

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The secondary outcome measure is the proportion of patients who achieve the ability to walk without assistance, defined as taking at least five
steps independently while displaying coordination and balance.

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Developmental abilities, including motor function, will be evaluated as exploratory objectives.

Outcome Measures for Patients Between 24 and 60 Months of
Age

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The primary outcome measure for patients between 24 months and 60 months of age at the time of dosing is the achievement of
change in Hammersmith Functional Motor Scale Expanded from baseline.

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The secondary outcome measure is the proportion of patients who achieve the ability to walk without assistance, defined as taking at least five
steps independently displaying coordination and balance.

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Developmental abilities, including motor function, will be evaluated as exploratory objectives.

The
trial is projected to be conducted at 11 sites in the United States, including Ann and Robert H. Lurie Children's Hospital of Chicago, Boston Children's Hospital, Children's
Hospital of Philadelphia, David Geffen School of Medicine at UCLA, Johns Hopkins Pediatric Neurology, Nationwide Children's Hospital, Stanford University Medical Center, University of Central Florida